These studies have been set up to evaluate the effectiveness of a gonadotropin releasing hormone antagonist in men. The men will be given a GnRH antagonist alone (single dose studies and 21 day studies) or in conjunction with testosterone enanthate. This GnRH antagonist, supplied by Drs. Vale and Rivier, has been shown to be more 2-fold more potent than the reference compound. Therefore, this antagonist has a greater margin of safety. The studies are to be done in three parts as follows: 1. Single dose studies to establish dose response curves, monitor side effects, duration of the inhibitory effects and to select the doses to be used in the following studies. 2. 21-day studies to determine minimum inhibitory dose and compare intermittent daily doses with constant infusion of the antagonist during this phase. 3. Long term-16 week-studies to assess the efficacy of combined GnRH antagonist and testosterone. Time frame was selected in view of the 70 day sperm cycle.